Can we remove our Account Address from the Chain, so it no longer works.
It is not possible to remove an account from the chain.
You can drain it of CCD or replace account keys, but you cannot delete it.
In case of data leak. If singing key used for basicAccountSigner in nodeJS get into wrong hand. Can we remove/update that sign-key?
Yes, the key can be changed, although the nodeJS SDK does not have that functionality implemented for you.
concordium-client supports this using an account update-keys subcommand Concordium Client transactions — Concordium documentation
But that’d mean you need to import your old keys into concordium-client.